According to the state of the art, automatic transmissions, particularly for motor vehicles, comprise planetary gear sets, which are shifted by means of friction and/or control elements, such as clutches and brakes, which are typically connected to a starting element subject to a slip effect and optionally provided with a lock-up clutch, for example, a hydrodynamic torque converter or a fluid clutch.
A transmission of this type is disclosed in EP 0 434 525 A1. It is essentially comprised of an input shaft and an output shaft, which are arranged parallel to one another, a double planetary gear set arranged concentrically to the output shaft, and five shifting elements in the form of three clutches and two brakes whose selective engagement in pairs respectively defines the different gear ratios between the input shaft and output shaft. In this case, the transmission has a front-mounted gear set and two power paths so that by selective meshing of pairs the five shifting elements, six forward gears are accomplished.
In this regard, two clutches are required in the first power path for the transmission of the torque of the front-mounted gear set to the two elements of the double planetary gear set. They are essentially arranged in the direction of the force flow behind the front-mounted gear set toward the double planetary gear set. Another clutch is provided in the second power path that detachably connects it with a further element of the double planetary gear set. In this case, the clutches are connected, such that the inner disk carrier forms the output element.
Furthermore, a compact multi-stage transmission of planetary design, in particular for a motor vehicle, is known from document U.S. Pat. No. 6,139,463, which has two planetary gear sets and a front-mounted gear set as well as three clutches and two brakes. In this known multi-stage transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting the torque from the front-mounted gear set to both planetary gear sets. The outer disk carrier and/or cylinder and/or piston and the pressure equalization side of the clutch C-3 is connected to a first brake B-1. In addition, the inner disk carrier of the third clutch C-3 is connected to the cylinder and/or piston and pressure equalization side of the first clutch C-1, whereby the inner disk carrier of the first clutch C-1 is positioned on the output side and connected to a sun gear of the third planetary gear set.
Furthermore, a multi-stage transmission is known from DE 199 49 507 A1 by the applicant in which two non-shiftable front-mounted gear sets are provided on the input shaft, which on the output side generate two rotational speeds that, apart from the rotational speed of the input shaft, can be selectively shifted to a shiftable double planetary gear set acting on the output shaft by selectively engaging the shifting elements which were used, such that only one shifting element must be engaged or disengaged for changing from one gear to the next higher or lower gear of the two just actuated shifting elements.
From DE 199 12 480 A1, an automatic motor vehicle transmission is known with three single-carrier planetary gear sets, as well as three brakes and two clutches for shifting six forward gears and one reverse gear, and an input shaft and an output shaft. The automatically shiftable motor vehicle transmission is configured such that the input shaft is directly connected to the sun gear of the second planetary gear set and that the input shaft can be connected, via the first clutch, to the sun gear of the first planetary gear set and/or, via the second clutch, to the carrier of the first planetary gear set. Additionally or alternatively, the sun gear of the first planetary gear set can be connected, via the first brake, to the transmission housing, and/or the carrier of the first planetary gear set can be connected, via the second brake, to the housing, and/or connected to the sun gear of the third planetary gear set, via the third brake to the housing.
Moreover, from DE 102 13 820 A1, a multi-speed transmission is known, comprising a first input path T1 of a first transmission ratio, an input path T2 that has a higher transmission ratio than this input path T1, a planetary gear set with four elements, whereby the four elements are a first element, a second element, a third element and a fourth element in the sequence of the elements in a rotational speed diagram, a clutch C-2 that transfers the rotation from the input path T2 to the first element S3, a clutch C-1 that transfers the rotation from the input path T2 to the fourth element S2, a clutch C-4 that transfers the rotation from the input path T1 to the first element, a clutch C-3 that transfers the rotation from the input path T1 to the second element C3, a brake B-1 that generates the mesh of the second element, a brake B-2 that generates the mesh of the second element, and an output element that is coupled to the third element R3.
In the context of DE 101 15 983 A1 by the applicant, a multi-stage transmission is described that has an input shaft that is connected to a front-mounted gear set, an output shaft that is connected to a rear-mounted gear set, and a maximum of seven shifting elements by means of whose selective shifting at least eight forward gears can be shifted without group shifting. The front-mounted gear set is formed by a front-mounted planetary gear set or a maximum of two non-shiftable front-mounted planetary gear sets coupled to the first front-mounted planetary gear set, whereby the rear-mounted gear set is configured as a double-carrier four-shaft transmission with two shiftable rear-mounted planetary gear sets and four free shafts. The first free shaft of this double-carrier four-shaft transmission is connected to the first shifting element, the second free shaft with the second and third shifting elements, the third free shaft with the fourth and fifth shifting elements, and the fourth free shaft is connected to the output shaft. The invention additionally proposes connecting the third free shaft or the first free shaft of the rear-mounted gear set to a sixth shifting element for a multi-stage transmission with a total of six shifting elements. The invention also proposes connecting the third free shaft to a sixth shifting element D′ and additionally the first free shaft to a seventh shifting element for a multi-stage transmission with a total of seven shifting elements.
A multi-stage transmission with at least seven gears is described within the scope of DE 101 15 987 by the applicant. Apart from the input shaft and the output shaft, this transmission consists of a non-shiftable, front-mounted gear set and a shiftable, rear-mounted gear set in the form of a double-carrier, four-shaft transmission. The front-mounted gear set consists of a first planetary gear set which, apart from the rotational input speed of the input shaft, offers a second rotational speed that can be selectively shifted to a rear-mounted gear set. The rear-mounted gear set consists of two shiftable planetary gear sets that can shift at least seven gears with the six shifting elements forming two power paths. In this case, group shifting is advantageously prevented with each shifting operation. A 9-gear, multi-stage transmission is further known from DE 29 36 969 comprising eight shifting elements and four gear sets.
Automatically shiftable vehicle transmissions of a planetary design have in general been described in the state of the art on many occasions and are subject to continuous development and improvements. Thus, these transmissions are supposed to require low design and construction costs, in particular, a small number of shifting elements, and prevent double shifts during sequential gear changes, so that only one shifting element at a time is changed when shifting in defined gear groups.
Previous planetary gear transmissions normally have only one reverse gear, whereas planetary gear transmissions are also known that have additional reverse gears that can either be shifted with the shifting elements available in the planetary gear transmission or implemented by means of an additional changing set. Thus, the disadvantage of the known planetary gear transmissions is either the insufficient number and inadequate transmission ratio of the reverse gears or the design and construction costs required for implementing the reverse gears.